Returns the m-th symmetric power of the differential operator L
as an element of the parent of L.
The symmetric power is monic where possible.
If n denotes the order of L, then
the degree of the m-th symmetric power of L
is at most (n + m - 1)choose(n - 1).
The algorithm that is used is based on algorithms given in [BMW97].
> F<z> := RationalDifferentialField(Rationals());
> R<D> := DifferentialOperatorRing(F);
> SymmetricPower(D^2, 3);
D^4
> SymmetricPower(D^3-1, 2);
D^6 + -7*D^3 + -8
V2.28, 13 July 2023